Hantaviruses are considered Category A Priority Pathogens by the National Institute of Allergies and Infectious Disease. These viruses cause a spectrum of vascular-leak syndromes including hantavirus pulmonary syndrome (HPS) and hemorrhagic fever with renal syndrome (HFRS). Many HPS and HFRS hantaviruses pose a natural threat to persons working, living or traveling in endemic regions, including military personnel. There is one hantavirus (Andes virus) that has unique properties that make amenable to use as a biological weapon.
Andes virus (ANDV) and Sin Nombre virus (SNV) are the predominant causes of HPS in South and North America, respectively. These rodent-borne viruses were discovered in the early 1990's and have caused severe disease in several hundred persons.
Since the discovery of SNV in 1993, it has caused severe disease in ˜500 persons in the United States and Canada, resulting in ˜200 deaths (35% case-fatality rate). SNV is carried by the deer mouse and transmitted via inhalation or ingestion of contaminated secreta/excreta, or by rodent bite. Most of the fatalities occurred in previously healthy working-age males. HPS is a disease with rapid onset, and rapid progression from mild to severe disease (i.e., can occur over the weekend). The disease begins as an influenza-like illness including fever, headache, nausea, cough, and can progress rapidly to respiratory failure and cardiogenic shock. There is no specific therapeutic or vaccine to treat or prevent HPS. Hammerbeck, C. D., Wahl-Jensen, V., Hooper, J. W. Hantavirus. In: Vaccines for Biodefense and Emerging and Neglected Diseases (A. D. T. Barrett and L. R. Stanberry, Eds.), pp. 379-411. London: Academic Press, 2009; Jonsson C. B, J. Hooper, and G. Mertz (2008). Treatment of hantavirus pulmonary syndrome. Antiviral Res. Antiviral Res. 78:162-169.
There is no population with pre-existing immunity to SNV or ANDV and this virus is lethal in 35-40% of the people it infects. Note that this 35-40% case-fatality rate occurs despite treatment in modern intensive care units. All ages and both sexes are susceptible to ANDY and SNV. Most cases occur in previously healthy working-age males. The incubation period is approximately two weeks. Disease onset-to-death is rapid (over the weekend). In an animal model of HPS (Syrian hamsters), ANDY is highly lethal by all routes tested including the oral route. SNV is highly infectious (infectious dose 50% is 2 plaque forming units in Syrian hamsters but does cause lethal disease (Hooper et al., 2001). Thus, an infection model, rather than a lethal disease model, is used to evaluate medical countermeasures to prevent SNV infection.
New-World hantaviruses have been associated with outbreaks of a highly lethal disease, hantavirus pulmonary syndrome (HPS), in the Americas (reviewed in Schmaljohn and Hjelle, 1997, Emerg. Infect Dis. 3, 95-104). The disease is characterized by fever and vascular leakage resulting in non-cardiogenic pulmonary edema followed by shock. Case-fatality for HPS caused by the most prevalent North American and South American hantaviruses, Sin Nombre virus (SNV) and Andes virus (ANDY), respectively is 30-50%.
Currently, there are four known hantaviruses associated with hemorrhagic fever with renal syndrome (HFRS): Hantaan virus (HTNV), Dobrava-Belgrade virus (DOBV), Puumala virus (PUUV), and Seoul virus (SEOV). Because distinct hantaviruses are usually carried by only one principal rodent host species, their distribution is generally limited to the range of that host (reviewed in Schmaljohn and Hjelle, 1997, Emerg. Infect. Dis. 3, 95-104). HTNV, carried by Apodemus agrarius, is found in Asia; DOBV, carried by Apodemus flavicollis, and PUUV, carried by Clethrionomys glareolus, are found in Europe. SEOV is more widely disseminated than any other recognized hantaviruses because its host, the common urban rat (Rattus norvegicus), is found throughout the world.
There is an alarming paucity of existing medical countermeasures to prevent or treat HPS. There is no vaccine against SNV, ANDY or any other HPS-associated hantavirus. Moreover, aside from basic research, there are no funded HPS vaccine development efforts. There is no specific drug to prevent or treat HPS. The treatment for HPS is extracorporeal membrane oxygenation therapy (ECMO) with costs as much as $500,000 per patient. Expertise at performing adult ECMO resides at only a few hospitals in the world. Thus, we are poorly prepared to deal with naturally occurring HPS cases (there have been ˜2500 cases including ˜500 in the US since 1993), or the use of hantaviruses as biological weapons.
Viruses in the Hantavirus genus (family Bunyaviridae) are enveloped and contain a genome comprised of three single-stranded RNA segments designated large (L), medium (M), and small (S) based on size (reviewed in Schmaljohn, 1996, In The Bunyaviridae Ed. R. M. Elliott. New York, Plenum Press p. 63-90). The hantavirus L segment encodes the RNA dependent RNA polymerase, M encodes two envelope glycoproteins (G1 and G2, also known as Gn and Gc), and S encodes the nucleocapsid protein (N).
A number of inactivated HFRS vaccines derived from cell culture or rodent brain were developed and tested in Asia (Lee et al., 1990, Arch. Virol., Suppl. 1, 35-47; Song et al., 1992, Vaccine 10, 214-216; Lu et al., 1996, J. Med. Virol. 49, 333-335). Drawbacks of these traditional killed-virus vaccines include a requirement for appropriate containment for the growth and manipulation of virus, and the necessity to ensure complete inactivation of infectivity without destroying epitopes on the virion important for protective immunity. In order to overcome these drawbacks, vaccine approaches involving recombinant DNA technology were developed including: vaccinia-vectored vaccines (Schmaljohn et al. 1990, J. Virol. 64, 3162-3170; Schmaljohn et al. 1992, Vaccine 10, 10-13; Xu et al. 1992, Am. J. Trop. Med. Hyg. 47, 397-404), protein subunit vaccines expressed in bacteria or insect cells (Schmaljohn et al. 1990, supra; Yoshimatsu et al., 1993, Arch. Virol. 130, 365-376; Lundkvist et al., 1996, Virology 216, 397-406), and a hepatitis core antigen-based recombinant vaccine (Ulrich et al., 1998, Vaccine 16, 272-280). For a review of hantavirus vaccine efforts see the review by Hooper and Li (Hooper and Li, 2001); Hammerbeck, C. D., Wahl-Jensen, V., Hooper, J. W. Hantavirus. In: Vaccines for Biodefense and Emerging and Neglected Diseases (A. D. T. Barrett and L. R. Stanberry, Eds.), pp. 379-411).
Vaccination with vaccinia recombinants expressing the M segment of either HTNV or SEOV elicited neutralizing antibodies and protected rodents against infection with both HTNV and SEOV, suggesting that an immune response to Gn-Gc alone can confer protection (Schmaljohn et al. 1990, supra; Xu et al. 1992, supra; Chu et al. 1995, J. Virol. 69, 6417-6423). Similarly, vaccination with Gn-Gc protein expressed in insect cells (baculovirus recombinant virus system) elicited neutralizing antibodies and protected hamsters from infection with HTNV (Schmaljohn et al. 1990, supra). In both the vaccinia and baculovirus systems, vaccination with Gn-Gc provided more complete protection than Gn or Gc alone (Schmaljohn et al. 1990, supra). There are reports that candidate DNA vaccines comprised of around 500 nucleotide stretches of the Sin Nombre virus (SNV) M gene, or the full-length S gene, are immunogenic in mice (Bharadwaj, et al., 1999, Vaccine 17, 2836, 43) and conferred some protection against infection with SNV in a deer mouse infection model (Bharadwaj, et al., 2002, J. Gen. Virol. 83, 1745-1751). The protection was surmised to be cell-mediated because there was no convincing evidence that these constructs elicited a neutralizing, or otherwise protective, antibody response.
There have been several publications reporting the successful use of plasmid DNA vaccines containing the full-length M gene of SEOV, HTNV, ANDV, including the following reports:    1. Hooper, J. W., K I Kamrud, F. Elgh, D. Custer, and C. S. Schmaljohn (1999). DNA vaccination with hantavirus M segment elicits neutralizing antibodies and protects against Seoul virus infection. Virology, 255:269-278.    2. Hooper, J. W., D. Custer, E. Thompson, and C. S. Schmaljohn (2001). DNA Vaccination with the Hantaan virus M gene protects hamsters against three of four HFRS hantaviruses and elicits a high-titer neutralizing antibody response in rhesus monkeys. Journal of Virology 75:8469-8477.    3. Custer, D. M., E. Thompson, C. S. Schmaljohn, T. G. Ksiazek, and J. W. Hooper (2003). Active and passive vaccination against hantavirus pulmonary syndrome using Andes virus M genome segment-based DNA vaccine. Journal of Virology 79:9894:9905.    4. Hooper, J. W., D. M. Custer, J. Smith, and Victoria Wahl-Jensen. Hantaan/Andes virus DNA vaccine elicits a broadly cross-reactive neutralizing antibody response in nonhuman primates (2006). Virology 347:208-216.
In all cases high titer neutralizing antibodies were detected in animals (including nonhuman primates) vaccinated with the full-length M gene DNA vaccines, and protection from infection was achieved in rodent models. Neutralizing antibody responses to Gn-Gc in the aforementioned vaccine studies correlated with protection, suggesting that neutralizing antibodies not only play an important role in preventing hantavirus infection, but also might be sufficient to confer protection. Passive transfer of neutralizing monoclonal antibodies (MAbs) specific to either Gn or Gc protected hamsters against HTNV infection (Schmaljohn et al., 1990, supra; Arikawa et al., 1992, J. Gen. Virol. 70, 615-624), supporting the idea that neutralizing antibodies alone can confer protection. This is further supported by the finding that serum from nonhuman primates vaccinated using a gene gun with DNA vaccines containing the HTNV or ANDY full-length M genes protected hamsters from infection with HTNV or lethal disease caused by ANDY Custer, D. M., E. Thompson, C. S. Schmaljohn, T. G. Ksiazek, and J. W. Hooper (2003). Active and passive vaccination against hantavirus pulmonary syndrome using Andes virus M genome segment-based DNA vaccine. Journal of Virology 79:9894:9905). Similarly, sera from rabbits vaccinated with the ANDY M gene-based DNA vaccine using electroporation protected hamsters from a lethal challenge with ANDY (Hooper J. W., A. M. Ferro, and V. Wahl-Jensen Immune Serum Produced by DNA Vaccination Protects Hamsters Against Lethal Respiratory Challenge with Andes Virus (2008). Journal of Virology 82:1332-1338.)
Hitherto, attempts to produce vaccines that produce neutralizing antibodies against SNV have been unsuccessful. For instance, Hjelle et al. (U.S. Pat. No. 6,316,250) attempted to vaccinate with the entire SNV Gn or fragments of G1 to generated antibodies. However, their vaccine did not produce high titer neutralizing antibodies. There are currently no serious efforts to develop an HPS vaccine anywhere in the world, including SNV vaccine. (refs 17, 18 below) NIH is currently funding a handful of academic laboratories working on hantavirus basic research.
The inventors have produced DNA vaccines against other hantaviruses including Seoul virus (SEOV), Hantaan virus, (HTNV) Puumala virus (PUUV) and Andes virus (ANDY) (refs 1, 5 and 6 below). There are a number of issued and pending patents related to these vaccines (refs 23-26 below). SEOV, HTNV, and PUUV cause hemorrhagic fever with renal syndrome (HFRS). All of these DNA vaccines are based on the full-length M gene open reading frame that encodes the Gn and Gc proteins, and all of these vaccines elicit neutralizing antibodies in animal models. Neutralizing antibodies produced by DNA vaccination have been shown to protect against infection and disease in passive transfer studies (refs 3,4 below). In addition, the Hantaan and Puumala DNA vaccines have been tested in a phase 1 clinical trial (ongoing). The immunogenicity data generated in this phase 1 trial demonstrates that DNA vaccines against hantaviruses were capable of eliciting neutralizing antibodies in humans. This was the first time hantavirus neutralizing antibodies have been produced in humans using plasmid DNA. The overall seroconversion rate in this phase 1 trial was 43% (12 of 28). One of the most notable findings was that very high titers of neutralizing antibodies were achievable. Two of the peak anti-Hantaan virus titers were >1,000 and four of the peak anti-Puumala virus titers were >1,000. Neutralizing antibody titers as high as 10,240 were achieved for both Hantaan virus and Puumala virus.
The antibody response elicited by the hantavirus M gene-based DNA vaccines have been shown to cross-neutralize some, but not other hantaviruses. For example, the HTNV DNA vaccine was shown to elicit neutralizing antibodies against Seoul virus and Dobrava virus (a major cause of HFRS in the Balkans)(ref 1 below). In some cases the cross-neutralizing antibody response is produced in certain species using certain delivery technologies, but not others. This was the case with our ANDY DNA vaccine. When nonhuman primates were vaccinated with the ANDY DNA vaccine using a gene gun the sera contained antibodies that not only neutralized ANDY but also neutralized SNV and Black Creek Canal virus (ref. 3 below). Based on those results we concluded that the development of a SNV-specific DNA vaccine was unnecessary. However, recently we found that when rabbits were vaccinated with the ANDY DNA vaccine using muscle electroporation the sera was unable to neutralize SNV despite exhibiting very high titer ANDY-neutralizing activity (ref 4 below). It is speculated that this could be due to antibody specificity differences, antibody avidity differences, or antibody isotype differences.
This finding prompted us to reinitiate the development of a SNV M gene-based DNA vaccine rather than depend on the ANDY DNA vaccine to cross-protect against SNV.
The inventor is named as an inventor on other U.S. patents and publications, related to vaccines for hantaviruses and poxviruses, namely U.S. Pat. Nos. 6,451,309; 6,620,412; 6,562,376, 7,217,812, and U.S. Patent application publication US-2010-03203024 A1. The entire contents of these patents are incorporated herein by reference.